1. Field of the Invention
The present invention relates to ingredients for use in pyrotechnic gas generant compositions, and more specifically to fuels containing a high oxygen balance. The gas generant compositions are useful as gas generant propellants for air bag occupant restraint systems for automobiles, gun propellants, inflation and expulsion devices, flotation devices, ignition materials, pyrotechnics, fire suppression devices and smokeless and smoke producing rocket propellants.
2. Background Art
There is high demand for pyrotechnic gas generant compositions which on combustion yield acceptable burning rates and provide, at relatively low flame temperatures, a high volume of substantially non-toxic gas and a low volume of solid particulate matter that can produce smoke. It is also important that resulting solid by-products from the combustion of gas generant compositions be minimal, and the gaseous combustion products be substantially non-toxic, and non-corrosive. Various compositions of gas generants have been utilized in the past in an attempt to reach the above desirable characteristics.
U.S. Pat. No. 3,405,144 discloses a 1-azido-N,N,N'-trifluoroformamidine that is useful in a propellant composition which exhibits a high specific impulse. Specifically, the said material is disclosed to be useful in rocket fuel compositions.
Gas generant compositions have also been developed to include the addition of modifiers to lower flame temperatures and increase gas production. Further ingredients may be added such as binders, ignition aids, slag formers, scavengers, and catalysts to improve various features of the underlying propellant. The modifiers and additional ingredients often times, however, improve one aspect of the propellant composition while also contributing to the production of undesirable by-products and may increase the corrosiveness thereof. This is particularly disadvantageous in an automobile air bag environment.
One major gas generating composition having desirable characteristics contains strontium nitrate and 5-aminotetrazole (SrN/5ATZ) as major constituents. This formulation is relatively non-toxic when compared with sodium azide systems, has good ballistic properties and retains the majority of solid combustion products as a slag or clinker either in the combustion or filtration areas of, for instance, an air bag system for an automobile. These formulations also exhibit acceptable flame temperatures of 2250.degree. K to 2750.degree. K depending upon the stoichiometry of the formulation and the oxygen to fuel ratio. Moreover, the strontium nitrate and 5-aminotetrazole formulations are relatively non-hygroscopic and the ingredients do not exhibit crystalline phase changes over the operating temperature range of the air bag system.
Such a formulation, however, suffers with regard to gas output, specifically, in the volume limited systems of a driver's side air bag. This is because a high concentration of strontium nitrate is required to maintain a neutral oxygen to fuel (O/F) balance. Because inflator designs are becoming smaller and smaller and, thus, more volume limited, propellants are required to provide greater gas output and still retain the desirable attributes of the strontium nitrate/5-aminotetrazole systems.
Approaches have been taken to obtain the attractive features of the above-noted propellants, while overcoming the low gas output thereof. This has resulted in the development of propellants based on mixtures of potassium perchlorate and oxygenated fuels such as guanidine nitrate and aminoguanidine nitrate. These propellants are also relatively non-hygroscopic, provide excellent gas output, high burning rates and only about two thirds of the solid combustion products of the above-noted strontium nitrate and 5-aminotetrazole based propellants. Unfortunately, the solid combustion products do not form clinkers or slags which deposit in the combustion or filtration area, but instead form very fine particulates in the gas stream which results in a smokey and dirty exhaust.
Smoke or dirty exhaust combustion products are not commercially desirable, particularly, in automobile air bag systems since the production of such product may cause undue anxiety on the part of drivers and passengers involved in an automobile accident in which air bags are deployed. As a result, there is a need for a propellant material or gas generant that exhibits high gas output upon combustion, but does not produce unwanted by-products upon combustion.